I assume by "server", you mean a computer, and not the "application server" that they run inside (usually Tomcat. Do not try to run different Atlassian applications in one Tomcat, it does not work)
The answer if you do mean "a computer", is "yes", but you're going to need to look at resources very carefully. The main resource is memory - you are going to need the server to have enough memory to run each application separately, and leave enough for the operating system and any other systems it's running. The next important resource is CPU, but that's more complex than just adding up maximum sizes. You're going to want a powerful one though, if you're running three on the same machine
But there's no way to know what the actual resource requirement will be unless you know how you're going to use it. If all three are really low usage, then you'd probably be ok with 4Gb RAM (a GB for each item to run), but if you're looking at more than 25 users and/or lots of builds, you're almost certainly going to need more. Probably a lot more.
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